The area of the caldera is now mainly covered by Mamaku Ignimbrite from the Mamaku eruption of 240,000 years ago that formed the Rotorua Caldera, but there are four earlier major ignimbrite eruptions of the Taupō Volcanic Zone that would have also contributed to its infilling.

[3]: 98 Eruptions from the Omanawa Caldera would explain formations such as the Waiteariki ignimbrite which covers much of the Bay of Plenty and forms the bulk of the Whakamarama Plateau.

[3]: 73  However, there are at least eight large eruptions that occurred in the Tauranga Volcanic Centre between 2.4 and 1.9 million years ago and at this time which ones relate to this caldera can not be definite.

[3]: 104  The Mangakino caldera complex which started forming 1,620,000 years ago,[6] to the southwest, is part of the old Taupō Volcanic Zone and more recent than the postulated Omanawa Caldera so fits with modelling of Taupō Rift extension to the south west towards Hauhungatahi in the period 2,100,000 to 900,000 years ago.

[3]: 22  There is no definite rhyolite dome relationship here and the geological structures observed to date in the southern Kaimai Ranges do not suggest a caldera underlies the southern Kaimai's, which have been suggested as another Tauranga Volcanic Centre caldera.